Sole electrode of the crossed-field type of electron discharge device having a coating of refractory material thereon



3,374,389 CTRON March 19, 1968 P. CAHOUR ETAL SOLE ELECTRODE OF THE CROSSED-FIELD TYPE OF ELE DISCHARGE DEVICE HAVING A COATING OF REFRACTORY MATERIAL THEREON Filed July 20, 1964 mdI mdE E g fizz/5455995555155956.

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ATTORN EY United States Patent 3,374,389 SOLE ELECTRODE OF THE CROSSED-FEELD TYPE OF ELECTRON DISCHARGE DEVICE HAVING A COATING OF REFRACTORY MA- TERIAL THEREON Pierre Cahour and Walter Sohotka, Paris, France, assignors to -CSF-Compagnie Gcnerale de Telegraphic Sans Fil, Paris, France Filed July 20, 1964, Ser. No. 383,634

Claims priority, application France, Aug. 6, 1963,

12 Claims. bi. s1s-3.s

ABSTRACT OF THE DISCLOSURE A crossed-field electron discharge device having a wave delay structure secured to an insulating base and a metallic sole electrode facing the delay structure, the surface of the sole electrode being coated with a refractory layer having a low electrical conductivity at least on the surface thereof.

The present invention relates to electron tubes with crossed electric and magnetic fields; that is, to those tubes in which the electron beam propagates between a delay circuit carried at a positive potential and a sole carried at a negative potential, an electric field being thus established between these electrodes by the presence of this potential difference, and a magnetic field being established across the inter-electrode space perpendicularly to this electric field and to the direction of propagation of the beam.

It is known that an electron beam traversing an imperfect vacuum ionizes the residual gases. In the tubes .plate or the envelope by an interval of air. The thickness of the deposited metal 'in effect brings about a growth of the metal of the delay circuit, without any other undesirable phenomenon.

However, it is different when the delay. circuit is fixed onto an insulating base as it is the case in certain known tubes for very high frequencies. In this case, the metal projections extractedlby sputtering" are deposited on the insulating surfaces between the metallic elements of the circuit, and by short-circuiting the same, or at least by introducing into the line an attention which progressively increases with aging of the tube, finishes by bringing to an end its operation, thereby reducing the longevity or length of life thereof.

The aim ofthe present invention is to eliminate this inconvenience by an improvement capable firstly of reducing the sputtering, and secondly of reducing, if not altogether eliminating, the harmful efr'ects which the residual sputtering is still capable of exercising on the delay circuit fixed onto an insulating base.

According to the present invention, the sole of a crossedfield tube, in particular, of the type in which the delay circuit isfixed to an insulating base, is covered with a thin layer of refractory insulating material to which is imparted the property whereby the positive charges, created by the secondary emission of the insulation, flow therethrough. For example, the insulation may be rendered slightly conductive, or still the insulation layer could receive an extremely thin, microporous structure within which the charges will flow 'by internal break-downs.

For example, one may cover the surface of the sole, by spraying of molten metal on the sole surface or plasma blow torch, with a layer of a substance of the type cerm et which is a known metal-ceramic mixture.

One may also dispose, also by spraying molten metal upon the surface to be coated or by plasma blow torch, a layer of refractory insulating material which one will cover with a superficial layer of a slightly conductive substance, such as colloidal suspension of graphite in water, known under the trademark Aquadagf As illustration of a possible modification, the insulation deposited on the sole may be porous, for example, of alumina, and in this case one will treat the sole covered with this insulating material in such a manner that an appropriate conductive substance is introduced into the pores of the insulating material. For example, one could impregnate the alumina with colloidal graphite very diluted in water. According to a still further modification, one may heat under pressure the sole covered with alumina within an oven with methane atmosphere, which will cause the methane to decompose in such a manner that the carbon derived from this decomposition will penetrate into the pores of the alumina.

According to another, still further modified embodiment of the present invention, one may cover a rigid base of copper or analogous material with a thin aluminum foil of which the superficial layer will be transformed, for example, by anodic oxidation into a micro-porous alumina layer of the order of 1 micron thickness. The application of the voltage between the delay circuit, and the sole produces in such a layer internal break-downs.

In all the cases, the structure described permits evacuaof the positive charges created by the secondary emission of the insulation, thereby avoiding the avalanche effect by secondary emission. The movement of the electron beam is thus not affected 'by the insulating layer.

When the sole is bombarded by the positive ions derived from the imperfect vacuum as indicated above, the sputtering is, in the first instance, largely diminished with respect to the prior art, for the pulverized material is refractory and vaporizes only with difiiculty. The residual sputtering only leads to the deposit on the insulating base of the delay circuit of a very reduced and poorly conductive layer which no longer exercises an important effect on the properties of the circuit and does-not reduce the length of life of the tube 'below the expected duration, fixed by other factors for limitation of its life/The present invention thus permits the reduction, if not the elimination, of the inconveniences indicated hereinabove.

Accordingly, it is an object of the present invention to provide a delay line structure, particularly for crossedfield tubes, which eliminates the shortcomings and drawbacks encountered with :the prior art constructions by extremely simple means and in an extraordinarily effective manner.

Another object of the present invention resides in the provision of a delay line structure or wave-retarding structure in which the harmful effects of any possible ion bombardment of an'eleotrode thereof, particularly of a negative electrode thereof, are significantly minimized, if not completely eliminated.

Still another object of the present invention resides in the provision of a delay circuit, fixed onto an insulated base, in which the danger of short-circuit by the deposit on the insulating material as a result of sputtering is completely eliminated.

Still a further object of the present invention-resides in the provision of a delay line structure, particularly for crossed-field devices, which effectively increases the length of life of the tube by reducing the effects of sputtering," and in particular by rendering harmless the effects of any residual sputtering that might still exist.

These and other objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration, two embodiments in accordance with the present invention, and wherein FIGURE 1 is a longitudinal cross-sectional view of the electrode system of a crossed-field tube, provided with the improvement according to the present invention;

FIGURE 2 is an enlarged detail of FIGURE 1; and

FIGURE 3 is an enlarged detail, similar to FIGURE 2, of a modified embodiment in accordance with the present invention.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURE 1, reference numeral 1 designates therein the metallic backplate to which is fixed an insulating base 2, onto which, in turn are fixed the metallic elements of the delay circuit 3. Facing the delay circuit 3 is disposed a sole 4 which, according to the present invention, is covered on its surface facing the delay circuit 3 with the very thin layer 5, of the order of 0.1 millimeter, for example, with a refractory insulating substance, rendered slightly conductive. According to FIGURE 2, the substance 5 is alumina that is, a porous refractory insulating material of which the pores 6 are filled with a conductive substance, for example, carbon, by any of the described methods or by any other known methods. According to the modified embodiment of FIGURE 3, the surface of the layer 5, facing the delay circuit 3, is covered with a layer 7 of some tens microns thickness, of a substance such as Aquadag.

One may also make the sole 4 of aluminum, disposed on another metal to render the structure sufficiently rigid, whereby the layer 5 is of alumina obtained by anodic oxidation of the aluminum, this layer being micro-porous and of a thickness of the order of one micron.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and we, therefore, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. A crossed-field electron discharge device, comprising:

an insulating base,

a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure,

the surface of said electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof.

2. A crossed-field electron discharge device, comprising:

an insulating base,

a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure,

the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof,

said refractory layer being a metal-ceramic mixture.

3. A crossedfield electron discharge device, comprising:

4 an insulating base, a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure, the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof, the refractory layer being an insulating material coated with a thin layer of a substance having a low electrical conductivity. 4. A crossed-field electron discharge device, comprising:

an insulating base, a Wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure, the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof, the refractory layer being an insulating material coated with a thin layer of a substance having a low electrical conductivity, said thin layer being made of a colloidal dispersion of graphite in Water. 5. A crossed-field electron discharge device, comprising:

an insulating base, a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure, the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof, the refractory layer being made of a porous insulating material whose pores are filled with a substance having a low electrical conductivity. 6. A crossed-field electron discharge device, comprising:

an insulating base, a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure, the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof, the refractory layer being made of a porous insulating material whose pores are filled with a substance having a low electrical conductivity, said insulating material being alumina. 7. A crossed-field electron discharge device, comprising:

an insulating base, a wave delay line structure secured to said insulating base, and a metallic sole electrode facing said delay line structure, the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof, the refractory layer being made of a'porous insulating material whose pores are filled with a substance having a low electrical conductivity, the pores of the insulating material being filled with carbon. 8. A crossed-field electron discharge device, comprising:

an insulating base,

a Wave delay line structure secured to said insulating base,

and a metallic sole electrode facing said delay line structure,

the surface of said sole electrode facing said' delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof,

the refractory layer being constituted by a very thin micro-porous insulating layer whose pores are sufficiently tenuous for electrical charges to discharge therethrough by electrical breakdown.

9. A crossed-field electron discharge device, comprismg:

an insulating base,

a wave delay line structure secured to said insulating base,

and a metallic sole electrode facing said delay line structure,

the surface of said sole electrode facing said delay line structure being coated with a refractory layer having a low electrical conductivity at least on the surface thereof,

the refractory layer being constituted by a very thin micro-porous insulating layer Whose pores are sufficiently tenuous for electrical charges to discharge therethrough by electrical breakdown,

said sole electrode having an aluminum portion and the micro-porous layer being aluminum oxide on the surface of the aluminum.

10. In an electron discharge device having a delay line secured to an insulating base and a metallic electrode facing the delay line which is subject to ion bombardment thereby producing sputtering effects jeopardizing the insulating properties of the insulating base,

the improvement essentially consisting of a metallic electrode structure provided with a thin layer of a refractory material having relatively low electrical conductivity.

11. In an electron discharge device having a delay line secured to an insulating base and a metallic electrode facing the delay line which is subject to ion bombardment thereby producing sputtering effects jeopardizing the insulating properties of the insulating base,

the improvement essentially consisting of a metallic electrode structure provided with a thin layer of a refractory material having relatively low electrical conductivity, and means in said refractory material to enable the flow therethrough of any charges due to secondary emission.

12. In an electron discharge device having a delay line secured to an insulating base and a metallic electrode facing the delay line which is subject to ion bombardment thereby producing sputtering effects jeopardizing the insulating properties of the insulating base,

the improvement essentially consisting of a metallic electrode structure provided with a thin layer of a refractory material having relatively low electrical conductivity,

said relatively thin layer having generally insulating characteristics with at least a portion thereof possessing relatively slight electrical conductivity properties.

References Cited HERMAN KARL SAALBACH, Primary Examiner.

35 S. CHATMON, JR., Assistant Examiner. 

